Vernier chopper controlling device

ABSTRACT

The armature current of a D.C. electric motor is controlled for power control by selectively shunting a plurality of series starting resistances, in order, which have resistance values such that the armature current, upon shunting, changes in value from a fixed starting current minimum to a permissible current maximum for each starting resistance, in combination with means for assuring that each of these current changes will be smooth and continuous over a substantial period of time by changing an effective series connected resistance an amount substantially equal to the starting resistance to be shunted, for each of the starting resistances in the order of their shunting. This means includes a current chopper in parallel electrical connection with a control resistance. The chopper may operate to pass current over a range identical for each shunting with variation of the control resistance to match the starting resistance to be shunted, or the control resistance may be identical for each shunting and the chopper current range may be matched to each of the resistances to be shunted.

United States Patent Ozawa Sept. 4, 1973 [57] ABSTRACT The armature current of a DC. electric motor is con- [75] Inventor: Tsutomu ozawa Katsuta Japan trolled for power control by selectively shunting a plu- 73 Assignee; Hi i L Tokyo, Japan rality of series starting resistances, in order, which have resistance values such that the armature current, upon [22] F'led: 1971 shunting, changes in value from a fixed starting current 21 L 20 ,321 minimum to a permissible current maximum for each starting resistance, in combination with means for assuring that each of these current changes will be [30] Forelgn Apphcamm Pnomy Data smooth and continuous over a substantial period of Dec. 29, 1970 Japan 45/128558 time by changing an effective series connected regigtance an amount substantially equal to the starting re- US. Clistance to be shunted for each of the tarting resist- Int. CL ances in order of their shunting means in- Field of Search cludes a current chopper in parallel electrical connec- 318/519, 520, 349, 380 tion with a control resistance. The chopper may operate to pass current over a range identical for each (defences Cited shunting with variation of the control resistance to UNITED STATES PATENTS match the starting resistance to be shunted, or the con- 3,ss1,172 5 1971 Tsuboi 318/259 resistance may be identical for each shunting and 1,895,924 1 1933 Hammond, Jr. 318/349 x the pp current range y be matched to each of 3,341,759 9/1967 Torii 318/422 the resistances to be shunted. 3,067,372 12/1962 Blanchard et a] 318/393 9 Claims, 5 Drawing Figures Primary Examiner-B. Dobeck Attorney-Thomas E. Beall, Jr.

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ARMATURE CURRENT .rzmmmzu wZFrmdFm Ommmm ZOPOE ARMATURE CURRENT 1 VERNIER CHOPPER CONTROLLING DEVICE BACKGROUND OF THE INVENTION In the power control of rotary electric machinery, particularly D.C. rotary electric machinery for the purposes of controlling rolling stock prime movers, for either acceleration, deceleration by dynamic braking, or speed control in general, it has been the practice to change the power circuit resistance in steps, stages or notches. Particularly, it was accepted practice to provide a plurality of starting resistances in series with the armature of the main D.C. electric motor of rolling stock prime movers for successively shunting the starting resistances for in turn increasing armature current upon shunting.

The U.S. Pat. to Blanchard et al. No. 3,067,372, issued 1962, is an example of the prior art wherein the successive starting resistance shunting is conducted such that the armature current will vary between a constant maximum and a constant minimum for each shunting, but this type of device has the considerable disadvantage that there will be an instantaneous current surge in the motor armature for each shunting, which will produce wheel slipping upon occasion and considerable discomfort to the passengers of the rolling stock vehicle.

To overcome such current surge problems, it has been the practice to provide a switching circuit or current chopper in parallel with a control resistance serially connected with the starting resistances so that immediately prior to shunting the effective line resistance of the chopper and control resistance may be varied an amount equal to the starting resistance to be shunted to change the current from its minimum to its maximum over a considerable period of time and avoid the abovementioned surging. However, with such a device it has been necessary to construct each of the starting resistances and control resistance to have the same resistance value to completely eliminate current surging during shunting. This has the undesirable affect of having a different armature current range for each shunting. An example of such a circuit is shown in the US. Pat. to Tsuboi No. 3,581,172, issued May 25, 1971, to the assignee of the present invention.

Further, it is known to selectively connect a current chopper in parallel with each of the starting resistances, in order, immediately prior to their shunting, as shown by the US. Pat. to Torii No. 3,341,759, issued 1967.

SUMMARY OF THE INVENTION It is an object of the present invention to provide power control for the armature of an electric motor used as a prime mover for rolling stock so that with the successive shunting of series connected starting resistances, the armature current will vary between a constant minimum and a constant maximum, by using a single variable resistance means in series with the starting resistances at all times. This variable resistance means preferably employs a current chopper in parallel with at least one control resistance. The effective resistance provided in series by the resistance control means may be changed by providing a constant current range chopper in parallel with a plurality of control resistances, some of which may be switched into and out of circuit to match the resistance of the starting resistance to be shunted, or by providing a fixed single control resistance at least as great as the largest starting resistance in combination with a current chopper whose chopping range may be controlled to match the current effect of the starting resistance to be shunted. Preferably, the minimum annature current will be the motor starting current and the maximum armature current will be the maximum level permissible for the electric motor.

BRIEF DESCRIPTION OF THE DRAWING Further objects, features and advantages of the present invention will become more clear from the following detailed description of the drawing, wherein:

FIG. 1 is a schematic electrical diagram of a control circuit employing the features of the present invention, for one preferred embodiment;

FIG. 2 is a schematic electrical diagram of a control circuit employing the features of the present invention, of a second preferred embodiment;

FIG. 3 is a motor speed-armature current plot for a control device similar to that shown in FIG. 1, but without the features of the present invention;

FIG. 4 is a motor speed-armature current plot for the control circuit of the present invention operating over a narrow armature current range as a small improvement over FIG. 3; and

FIG. 5 is a motor speed-armature current plot for the control circuit of the present invention operating over a wide armature current range between the starting current and the maximum permissible armature current.

DETAILED DESCRIPTION OF THE DRAWING One preferred embodiment of the present invention is used for motor control for a rolling stock prime mover, either for power control of the motor or for dynamic braking with the motor operating as a generator. That portion of the embodiment of FIG. 1 corresponding with the prior art will first be described with respect to its operation and its circuit characteristics as shown in FIG. 3.

In FIG. 1, a power source is provided by the conventional string voltage line 1, pantograph 2, circuit breaker (not shown) and main disconnect switch (not shown) in series with line 3 leading to a D.C.electric motor 4. For stepping control of the starting resistance, there are provided a plurality of separate serially connected starting resistances 5, 6, 7, 8, 9, l0 and a plurality of shunting switches 11, 12, 13, l4, l5, 16. These shunting switches may be solenoid control switches or SCR switches. In a conventional manner, the closing of normally open switch 11 would shunt or short-circuit resistor 5, the closing of switch 12 would short-circuit resistor 6, etc.

In series with the motor 4, there is additionally a resistance varying means 17 including a current chopper, current regulator or current divider 18 that may basically be of any conventional type, such as the switching circuit disclosed in the above-mentioned Tsuboi U.S. Pat. No. 3,581,172, whose disclosure is incorporated herein by reference in its entirety. The resistance varying means further includes a control resistance 19 and shunting switch 20, in parallel with each other and in parallel with the chopper 18.

In conventional operation of the device according to FIG. 1, the shunting switches 11-16 would normally be open at the starting of the main electric motor 4, and the flow passage rate of the chopper 18 would, for example, be effectively percent so that the entire value of the resistance 19 would be in series with starting resistances -10. Operation under these conditions would be denoted as the first stage or first notch. For moving from the first notch to the second notch, the flow passage rate of the chopper 18 would be gradually increased from 0 percent continuously to 100 percent, for example to effectively short-circuit the control resistance 19, which control resistance 19 would conventionally be equal in value to each of the equal starting resistances 5-10. Upon reaching the 100 percent rate for the chopper 18, the control resistance 19 would effectively be short-circuited, and the switch 1 1 would be closed to simultaneously short-circuit starting resistance 5; simultaneously the flow rate of the chopper 18 would be reduced substantially instantaneously to a 0 percent to again connect the full value of the resistance 19 in circuit. The same controlling pattern would be repeated to close the succeeding switches 12, 13, 14, 15, 16, in order, to successively short-circuit the starting resistances 6, 7, 8, 9, 10, respectively along with the appropriate operation of the chopper 18. This procedure would be determined by the controller 21 having control communication as indicated with the switches 11-16 and chopper 18.

The plot of FIG. 3 shows the notching curves obtained with the above-mentioned conventional portion of FIG. 1. The maximum permissible range of variation of the main electric motor current when the chopper 18 is turned on for 100 percent passage of current or off for 0 percent passage of current depends on the allowable pulsation factor of the main electric motor 4.

In FIG. 3, assuming that the fifth notch position has just been reached with switch closed and the chopper 18 off, the electric current of the main electric motor 4 will be 10, and will be IcS when the chopper is on and switch 15 closed. The range of such motor electric current variation is enlarged in proportion as the resistivity of the starting resistance connected in series to the chopper 18 is decreased, and at the moment when the seventh notch position is reached, such range will span from I0 to I0 7.

Noting the fact that the scope of variation of the starting current of the main electric motor is varied according to the resistivity of each starting resistance as mentioned above, the present invention has for its object to reduce the number of notches necessitated by making use of this fact.

According to the present invention, the values of the starting resistances 5-10 are all different and so chosen that when the chopper 18 is effectively in its off position immediately prior to each shunting operation, that is closing of switches 11-16 successively, the armature current will be the same, and when the chopper is in its effective on position or any one of the switches 11-16 has just been closed, thevmaximum armature current will be the same. Thus, the peak value of the starting current in each notch or control stage will remain constant.

To choose the value of the starting resistances, let it be assumed that the string voltage is E(V), the starting current is Io(A) and the velocity or motor speed of the eighth notch at that time is V8(I(m/h), and that the electric current when commutation of the chopper 18 has become fully effective is lc(A) and the velocity at that time is V8(Km/h). With these conditions being given, the resistivity of the resistance short-circuited by the switch 16 is obtained from the following equation wherein the value of the starting resistances are represented by R followed by their respective number:

Then, the velocity or speed for Ic(A) at seventh notch is obtained and it is assumed to be V6(l(m/h).

The resistivity of the resistance short-circuited by the switch 15 at that time is given from the following equation:

By following the above procedure in a similar manner, it is possible to obtain resistivities of the other resistances, down to the resistance R6 short-circuited by the switch 12.

If the values of the resistance in the starting resistance sections obtained in the manner described above are controlled or matched by the chopper 18 successively from the section with highest resistance, there will be obtained the notching curve as shown in FIG. 4. According to the plot of FIG. 4, the starting current 10 and the peak current Ic for each notch will be respectively constant, so that by bringing this peak value lc up to the maximum level permissible for the main electric motor, it is possible to reduce the number of notches necessary and correspondingly the number of switching stages and starting resistances as shown in FIG. 5. v

The first embodiment of the present invention for producing the above-desired results, with the plots of FIGS. 4 and 5 being applicable, employs the aboveidentified structure except that the values of the starting resistances 5-10 are all different and chosen so as to produce notching curves that in plots of motor speed versus armature current would produce the characteristics as shown in FIGS. 4 and 5 such that the intersections between a constant starting current line and the notch curves would directly correspond to the same speed with the intersections of a constant maximum current line and the next succeeding notch curve. In addition, the current passage range of the chopper 18 may be varied to produce different current ranges in number corresponding to the number of resistance steps or starting resistances 5-10. Further, each current passage range for the chopper 18 is such that it will, in parallel with the control resistance 19, produce a change in effective resistance for the means 17 substantially identical to the resistance of the associated starting resistances 5-10. While this is a specific example, it is, of course, recognized that the current passage for the chopper 18 may closely approximate the ultimate ranges to the point where the differences will produce negligible results with respect to current surge, for example, the end values for the chopper current transmission ranges may vary 10 percent. To obtain the best results by matching the change in effective resistance of means 17 with the starting resistance to be shunted, it is a feature of the present invention that the control resistance 19 is at least as large as the largest starting resistances 5-10, and may be larger.

By way of a specific example, with switch 13 closed and the motor speed increasing to the point where the back e.m.f. increases and reduces the armature current to the predetermined constant minimum, for example lo, the chopper 18 is off, that is does not pass any current. Upon reaching 10, it will be desired to proceed to the next notch. At this point, the controller in response to sensing the armature current reaching the minimum, that is reaching Io, will send a signal to the chopper 18 to increase its current transmission in a smooth and continuous manner to the point where it changes the effective resistance of means 17 an amount equal to the resistance to be shunted to correspondingly smoothly and continuously increase the armature current from Io to the maximum constant value, for example 10, over a period of time sufficient to prevent undesirable current surge and shock but over a time short enough such that it may be assumed that the motor speed does not increase. At the moment of reaching Ic by at least partially short-circuiting the control resistance 19 by the chopper 18, the controller closes switch 14 to shortcircuit starting resistor 8 and simultaneously reduces the current transmission of chopper 18 in a substantially instantaneously manner corresponding to the operation of the switch 14 to zero, that is turns chopper 18 off. Thus, the range of no current transmission to partial transmission for the chopper 18 is different for each notching position and is so chosen that together with the fixed control resistor 19 will produce an effective resistance change for the means 17 respectively matched to the starting resistors 5-10.

During the above switching, the switch 20 is normally open and will be closed at the end of the last notch to short-circuit the chopper l8 and the control resistor 19 when full motor speed is desired.

From the above, it is seen that it is one important feature of the present invention that the number of starting resistors or notches may be substantially decreased with respect to the number required in prior stepping resistor and chopper arrangements because the full armature current range between starting current and maximum permissible armature current may be utilized for each switching operation from starting resistor to the next starting resistor.

It is a second important feature of the present invention that the control resistor 19 is at least as large as the largest of the starting resistors. If this feature of the present invention were not complied with and the control resistor 19 was smaller in resistance value than the largest of the starting resistances, the current variation at the time of short-circuiting of this largest starting resistance would give rise to a current surge or shock for the entire system, which would manifest itself in an unpleasant sensation for vehicle passengers or perhaps an undesirable wheel slip. However, by making the control resistance at least as high as the highest starting resistance, it is possible to maintain the balance with the other starting resistors as well as the highest starting resistor by controlling the current transmission range of the chopper 18.

A third important feature of the present invention relates to the changing of the effective control resistance for the means 17 connected in parallel with a chopper having a fixed range of current transmission. This is accomplished according to the second embodiment shown in FIG. 2, which embodiment will produce plots identical to those shown in FIGS. 4 and 5. Those elements of FIG. 2 that are identical to the correspondingly numbered elements in FIG. 1 have been provided with primes to show a separate embodiment and the above description with respect to FIG. 1 will suffice for the same element in FIG. 2, with the following differences.

In FIG. 2, the controller 22, when operating under conditions such that switches 11', 12', 23, 24, and 20' are open will sense the time when the motor speed increases to the point where its back e.m.f. produces a reduction in armature current to the predetermined minimum current, for example the starting current of FIGS. 4 and 5, and at this time will send a signal to the fixed range chopper 25 to smoothly and continuously increase its current transmission to the point where it effectively short-circuits control resistor 19', which control resistor 19 is substantially equal in value to the starting resistor 5",thereafter, the controller 22 will simultaneously close the switch 11' to short-circuit the starting resistor 5', return the chopper 25 to substantially 0 transmission, and close switch 23 to place resistor 26 in parallel with control resistor 19 to produce an effective resistance for the means 17' that will be substantially the same as resistance for the starting resistor 6'. When the motor speed again increases to the point where the controller 22 senses the reduction of the armature current to lo, the chopper 25 is again actuated to function over its fixed range, after which the chopper is turned off simultaneously with closing of switches 12', 20'. In a manner similar to resistor 26 and switch 23, resistor 27 and switch 24 may be used when there is a third starting resistor.

The chopper 25 of FIG. 2 while operating over a fixed transmission range, may have such range be to 10 percent of full current transmission, rather than to 0 percent of full transmission, or the like variation. A further advantage of the embodiment of FIG. 2 is that the effective resistance placed in parallel with the chopper decreases as the effective starting resistance decreases.

Further, resistor 27 and switch 24 may be used with resistor 26 and switch 23 to change the effective fixed resistance of means 17 in steps for matching the second starting resistor. Also, the chopper may be used to smooth out the switching in and out of resistors 26 and 27.

Further embodiments, variations and modifications are contemplated according to the spirit and scope of the present invention, as defined by the following claims, although the specific details are important according to the more narrow aspects of the present invention.

What is claimed is:

l. A direct current rotary electric machine control circuit, comprising: a plurality of separate starting resistances in series and having different resistance values; means for placing said starting resistances in series with a source of electric power and a rotary D.C. electric machine for stepping power control; means for shunting each of said starting resistances in a predetermined order so that the thus controlled current minimum and maximum for each successive shunting re mains respectively constant as determined by the different starting resistance values; current chopper and resistance means in series with said starting resistances for changing in effective resistance smoothly over a period of time immediately prior to shunting each starting resistance, with the resistance change being difierent for each shunting and matched with the starting resistance to be shunted, and substantially instantaneously adding the same effective resistance at shunting.

2. The control circuit of claim 1, wherein said current chopper and resistance means includes at least one control resistance means in series with said separate starting resistances and having a resistance value at least as great as the greatest resistance value of said starting resistances, and further having a current chopper in parallel with said control resistance means and in series with said starting resistances.

3. The control circuit of claim 2, wherein said current chopper and resistance means controls the operation of said current chopper to vary the current passed therethrough in a continuous manner from a predetermined minimum to a predetermined maximum constituting a range, with the range for each shunting step being different.

4. The control circuit of claim 3, wherein said current chopper and resistance means controls the operation of said current chopper so that the first chopper range will effectively reduce the resistance of said control resistance means in series with said starting resistances an amount equal to the resistance of the first starting resistance shunted, and the second chopper range will effectively reduce the resistance of said control resistance means an amount substantially equal to the second starting resistance shunted.

5. The control circuit of claim 1, wherein said current chopper and resistance means includes a selectively variable resistance means in parallel with a fixed range current chopper and means for varying the variable resistance means to successively match each of said starting resistances, in order, as they are shunted.

6. The control circuit of claim 5, wherein said variable resistance means and means for varying include a plurality of separate resistances in parallel with each other and in parallel with said current chopper and switch means for connecting and disconnecting at least some of said parallel resistances in circuit.

7. The control circuit of claim 6, in combination with a direct current rotary electric machine having an armature in series connection with said starting resistances, and in series connection with said current chopper and resistance means; said armature having a maximum permissible current level equal to said maximum current; and said armature further having a designed starting current equal to said minimum current level.

8. The control circuit of claim 4, in combination with a direct current rotary electric machine having an armature in series connection with said starting resistances, and in series connection with said current chopper and resistance means; said armature having a maximum permissible current level equal to said maximum current; and said armature further having a designed starting current equal to said minimum current level.

9. The control circuit of claim 1, in combination with a direct current rotary electric machine having an armature in series connection with said starting resistances, and in series connection with said current chopper and resistance means; said armature having a maximum permissible current level equal to said maximum current; and said armature further having a designed starting current equal to said minimum current level. 

1. A direct current rotary electric machine control circuit, comprising: a plurality of separate starting resistances in series and having different resistance values; means for placing said starting resistances in series with a source of electric power and a rotary D.C. electric machine for stepping power control; means for shunting each of said starting resistances in a predetermined order so that the thus controlled current minimum and maximum for each successive shunting remains respectively constant as determined by the different starting resistance values; current chopper and resistance means in series with said starting resistances for changing in effective resistance smoothly over a period of time immediately prior to shunting each starting resistance, with the resistance change being different for each shunting and matched with the starting resistance to be shunted, and substantially instantaneously adding the same effective resistance at shunting.
 2. The control circuit of claim 1, wherein said current chopper and resistance means includes at least one control resistance means in series with said separate starting resistances and having a resistance value at least as great as the greatest resistance value of said starting resistances, and further having a current chopper in parallel with said control resistance means and in series with said starting resistances.
 3. The control circuit of claim 2, wherein said current chopper and resistance means controls the operation of said current chopper to vary the current passed therethrough in a continuous manner from a predetermined minimum to a predetermined maximum constituting a range, with the range for each shunting step being different.
 4. The control circuit of claim 3, wherein said current chopper and resistance means controls the operation of said current chopper so that the first chopper range will effectively reduce the resistance of said control resistance means in series with said starting resistances an amount equal to the resistance of the first starting resistance shunted, and the second chopper range will effectively reduce the resistance of said control resistance means an amount substantially equal to the second starting resistance shunted.
 5. The control circuit of claim 1, wherein said current chopper and resistance means includes a selectively variable resistance means in parallel with a fixed range current chopper and means for varying the variable resistance means to successively match each of said starting resistances, in order, as they are shunted.
 6. The control circuit of claim 5, wherein said variable resistance means and means for varying include a plurality of separate resistances in parallel with each other and in parallel with said current chopper and switch means for connecting and disconnecting at least some of said parallel resistances in circuit.
 7. The control circuit of claim 6, in combination with a direct current rotary electric machine having an armature in series connection with said starting resistances, and in series connection with said current chopper and resistance means; said armature having a maximum permissible current level equal to said maximum current; and said armature further having a designed starting current equal to said minimum current level.
 8. The control circuit of claim 4, in combination with a direct current rotary electric machine having an armature in series connection with said starting resistances, and in series connection with said current chopper and resistance means; said armature having a maximum permissible current level equal to said maximum current; and said armature further having a designed starting current equal to said minimum current level.
 9. The control circuit of claim 1, in combination with a direct current rotary electric machine having an armature in series connection with said starting resistances, and in series connection with said current chopper and resistance means; said armature having a maximum permissible current level equal to said maximum current; and said armature further having a designed starting current equal to said minimum current level. 